(1) Field of the Invention
This invention relates to a semiconductor integrated circuit used for an electronic machine such as a computer, and having a Dynamic Ram (DRAM) cell unit and a nonvolatile cell unit.
(2) Description of the Related Art
The conventional memories obtained by nonvolatilizing the information stored in a volatile memory include a NVRAM (Nonvolatile RAM) consisting of as shown in FIG. 3, a SRAM (Static RAM) 30 to which floating gate type memory transistors 33a, 33b are added. Referring to the drawing, reference numerals 31a, 31b denote bit lines, and 32a, 32b denote word lines.
It is difficult to subject a SRAM to high-density integration since the area of a memory cell therein is large.
As shown in Japanese laid Open Patent Tokkosho 62-185376 (Japanese application number sho 62-17450), the conventional memories obtained by nonvolatilizing the information stored in a volatile memory include a nonvolatile DRAM consisting as shown in FIG. 4 of a DRAM to which a second capacitor is added. Referring to the drawing, reference numerals 41 denotes bit line, 42 first capacitor, 43 transistor, 44 word line, 45, 47 lines, and 46 second capacitor comprised of a ferroelectric substance.
It is difficult to subject a first capacitor to a small capacity since a large parastic capacitance composed of a second capacitor 46 and a capacitor developed between a line 47 and ground therein is developed during operation of the DRAM.
As a result, it is difficult to subject a DRAM to high density integration since the area of a memory cell therein is large.